The subject invention relates methods and apparatus for monitoring electric arcs.
Power supply systems and other apparatus often introduce alternating current fundamentals into the chaotic spectra of arc signatures. In practice, this frequently impedes a reliable monitoring of electric arcs, and tends either to cause false alarms or to engender a certain insensitivity to the monitoring function.
The traditional response to that problem was to filter out such alternating current fundamentals in the region of the power supply or line frequency. That kind of approach, however, precluded the monitoring system from taking into account those increasingly important components of the chaotic arc signature that are in the frequency range of an alternating current fundamental. At the same time, harmonics of the filtered-out fundamentals could still cause false alarms. Countering such problem by filtering out harmonics in addition to the fundamentals, eliminated even more otherwise detectable components from the arc signature, rendering the arc monitoring process still more insensitive.
The problem was aggravated by the fact that the chaotic spectra of arc signatures are neither synchronous with, nor correlated to, line frequency fundamentals. This in effect precludes use of approaches that generally work well in alternating current distribution systems wherein load currents typically are synchronous with and correlated to the alternating current power frequency. Moreover, the arcing information in power distribution systems is on the electric current waveform which may not have any resemblance in shape to the voltage waveform at various times and load conditions. Accordingly, relying on a voltage waveform in deriving information about the line frequency fundamental or harmonics can cause further difficulties. Problems mount further if the load goes to zero so that there is no load current to rely on.
During two flights, first from west to east and then from east to west, the attorney of record herein made EMF (electromagnetic field) measurements aboard an MD-11 passenger aircraft and obtained the following results in milligauss:
It is to be noted in this respect that the MD-11 model has a third jet engine in the rear, and has a galley between the two rear lavatories.
Since there was no evidence of any arcing at the time, it may be assumed that what the gauss meter measured were fundamentals and harmonics of the aircraft""s 400 Hz power supply or other regularly occurring oscillations. Since the galley on that aircraft has heavy electric cooking appliances on its starboard side, it appears that the comparatively heavy EMF crosswise readouts in the starboard side rear lavatory may represent fluctuating values, as the crew prepared food for the passengers when the starboard side measurements were taken.
Such and similar fundamentals, harmonics and fluctuating signals of a non-chaotic nature regularly occurring aboard aircraft or on ships, land vehicles or installations and the like, should be taken into account or eliminated when monitoring arcs or sparks there, and their effect should be countered in devising arc or spark monitoring equipment.
It is a general object of the invention to overcome the drawbacks and to meet the needs set forth above or otherwise expressed or implicit in this disclosure.
It is a germane object of the invention to provide improved electric arc monitoring systems.
It is a related object of the invention to provide electric arc monitoring systems which avoid false alarms from alternating current fundamentals and harmonics.
Other objects of the invention will become apparent in the further course of this disclosure.
From a first aspect thereof, the invention resides in a method of monitoring electric arcs having arc signatures including an alternating current fundamental and harmonics in addition to chaotic components characteristic of such arcs, comprising, in combination, phase shifting, delaying or otherwise storing a representation of the alternating current fundamental and harmonics, substantially purging such alternating current fundamental and harmonics from the arc signatures with the stored representation of such alternating current fundamental and harmonics, while substantially preserving the chaotic arc signatures components, and monitoring the electric arcs from the purged arc signatures.
From a related aspect thereof, the invention resides in apparatus for monitoring electric arcs having arc signatures including an alternating current fundamental and harmonics in addition to chaotic components characteristic of such arcs, comprising, in combination:, an electric arc pickup, an alternating current fundamental and harmonics phase shifter, delay or other storage having an input connected to the electric arc pickup and having an output, a summing network having a first input connected to the electric arc pickup and an oppositely poled second input connected to the output of the alternating current fundamental and harmonics phase shifter, delay or other storage and having a summing network output, and an electric arc monitor connected to that summing network output.
Within the scope of the invention, the alternating current fundamental and harmonics phase shifter, delay or other storage may include means for phase shifting, delaying or otherwise storing a representation of the alternating current fundamental and harmonics, and the summing network may include means for substantially purging said alternating current fundamental and harmonics from the arc signatures with such phase shifted, delayed or otherwise stored representation of the alternating current fundamental and harmonics, while substantially preserving the chaotic arc signature components, and the electric arc monitor may include means for monitoring the electric arcs from the purged arc signatures.
However, there is no reason in the subject disclosure and in any of the claims, other than in the first dependent means plus function apparatus claim, to consider any of the claims other than that first dependent means plus function apparatus claim to be limited in any manner pursuant to the sixth paragraph of 35 USC 112.
Also, the expression xe2x80x9cstoragexe2x80x9d when used as a noun in this disclosure and in apparatus claims hereof is used in the broad sense of any device or apparatus in which information can be stored, such as confirmed in xe2x80x9cThe New IEEE Standard Dictionary of Electrical and Electronics Terms,xe2x80x9d of the Institute of Electrical and Electronics Engineers (1993), and in the xe2x80x9cMicrosoft Press Computer Dictionaryxe2x80x9d by Microsoft Corporation (1997).